The Antarctic ice sheet is a large ice cover that covers 98% of the Antarctic continent. It has an area of 14 million square kilometers (5.4 million square miles) and is more than 2 kilometers (1.2 miles) thick on average. It is the largest of Earth's two current ice sheets and holds 26.5 million cubic kilometers (6,400,000 cubic miles) of ice. This ice is equal to 61% of all fresh water on Earth. The ice sheet's surface is mostly continuous, and the only areas without ice are the dry valleys, exposed mountain peaks called nunataks, and some coastal rock areas. The ice sheet is often divided into three parts: the Antarctic Peninsula, the East Antarctic Ice Sheet, and the West Antarctic Ice Sheet. These areas differ in how much ice is gained or lost, how ice moves, and the shape of the land.
The East Antarctic Ice Sheet is over 10 times larger than the West Antarctic Ice Sheet and sits at a higher elevation. This makes it less affected by climate change compared to the West Antarctic Ice Sheet. In the 20th century, the East Antarctic Ice Sheet was one of the few places on Earth that showed slight cooling, while the West Antarctic Ice Sheet warmed by more than 0.1°C per decade from the 1950s to 2000. The whole continent has warmed by more than 0.05°C per decade since 1957. As of the early 2020s, the East Antarctic Ice Sheet still gains more ice than it loses because of increased snowfall freezing on its surface. However, glaciers in the West Antarctic Ice Sheet, such as Thwaites and Pine Island Glacier, are losing ice much faster.
By 2100, ice loss from Antarctica alone could raise global sea levels by about 11 centimeters (5 inches). The West Antarctic Ice Sheet is located deep below sea level, which makes it vulnerable to a process called marine ice sheet instability. This process is hard to model in computer simulations. If instability begins before 2100, it could increase sea level rise from Antarctica by tens of centimeters, especially if global warming is high. Antarctica loses about 1,100 to 1,500 billion tons of ice each year. This meltwater reduces the saltiness of deep Antarctic water, which weakens a key part of the Southern Ocean's circulation and could eventually cause it to collapse, though this may take many centuries.
Studies of past climates and better computer models show that the West Antarctic Ice Sheet is likely to disappear even if global warming stops. Reducing warming to 2°C below 2020 levels might help save it. Losing the ice sheet could take between 2,000 and 13,000 years, but high emissions over several centuries might shorten this to 500 years. If the ice sheet collapses but leaves mountain ice caps intact, global sea levels would rise by 3.3 meters (10 feet 10 inches). If those ice caps also melt, sea levels would rise by 4.3 meters (14 feet 1 inch). Over another 1,000 years, the rising of land after ice loss, called isostatic rebound, could add about 1 meter (3 feet 3 inches) to sea levels. In contrast, the East Antarctic Ice Sheet is much more stable and may only cause sea levels to rise by 0.5 to 0.9 meters (1 foot 8 inches to 2 feet 11 inches) from current warming levels. This is a small part of the 53.3 meters (175 feet) of ice stored in the entire ice sheet. If global warming reaches about 3°C (5.4°F), areas like Wilkes Basin and Aurora Basin could collapse over 2,000 years, adding up to 6.4 meters (21 feet) to sea levels. Losing the entire East Antarctic Ice Sheet would require global warming between 5°C (9.0°F) and 10°C (18°F).
Geography
The Antarctic ice sheet covers an area of about 14 million square kilometers (5.4 million square miles) and holds 26.5 million cubic kilometers (6,400,000 cubic miles) of ice. One cubic kilometer of ice weighs roughly 0.92 metric gigatonnes, which means the entire ice sheet weighs approximately 24,380,000 gigatonnes. This ice makes up about 61% of all fresh water on Earth. The only other ice sheet on Earth today is the Greenland ice sheet in the Arctic.
The Antarctic ice sheet is split into two unequal parts by the Transantarctic Mountains. These parts are called the East Antarctic Ice Sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS). Some scientists consider the ice on the Antarctic Peninsula, which is part of West Antarctica, as a third ice sheet because its drainage areas are different from the WAIS. Together, these ice sheets have an average thickness of about 2 kilometers (1.2 miles). Even the Transantarctic Mountains are mostly covered by ice, with only a few mountain peaks and the McMurdo Dry Valleys remaining ice-free today. Some coastal areas also have exposed rock that is not covered by ice. During the Late Cenozoic Ice Age, many of these areas were also covered by ice.
The EAIS sits on a large landmass, but the bed of the WAIS is, in some places, more than 2,500 meters (8,200 feet) below sea level. If the ice were not there, this area would be seabed. The WAIS is called a marine-based ice sheet because its bed lies below sea level and its edges flow into floating ice shelves. The WAIS is bordered by the Ross Ice Shelf, the Filchner-Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea. Thwaites Glacier and Pine Island Glacier are the two most important outlet glaciers.
Warming over the ice sheet
Antarctica is the coldest, driest, and highest continent on Earth. Its dry air contains very little water vapor and does not conduct heat well. The Southern Ocean around Antarctica absorbs more heat than any other ocean. The large, year-round sea ice around Antarctica reflects sunlight very well, adding to the brightness of the continent’s ice sheets. Antarctica’s cold temperatures cause a special weather pattern called an atmospheric temperature inversion to occur every winter. In most places on Earth, the air near the ground is warmer than the air higher up. In Antarctica, the ground becomes colder than the air above it during winter, which causes greenhouse gases to trap heat in the middle atmosphere. This effect continues until the end of winter. Early climate models predicted that temperature changes in Antarctica would happen more slowly and be less noticeable than in other places.
There were fewer than twenty permanent weather stations across Antarctica, and only two were located in the interior. Automatic weather stations were not widely used until later, and their records were short for much of the 20th century. Satellite temperature measurements began in 1981 but only work well when there are no clouds. Because of these challenges, complete temperature records for the entire continent were not available until the late 20th century. However, the Antarctic Peninsula showed clear signs of warming, with temperatures rising by 3 °C (5.4 °F) since the mid-20th century. Based on limited data, some studies from the early 2000s suggested that most of Antarctica had cooled slightly outside the Peninsula. A 2002 study led by Peter Doran found that the McMurdo Dry Valleys in East Antarctica had cooled by 0.7 °C per decade. The study noted its data was limited and still found warming in 42% of the continent.
The study received widespread media attention, with some reporters describing it as "contradictory" to global warming. Scientists criticized these descriptions. The controversy grew in 2004 when a book called State of Fear by Michael Crichton used the study to claim that climate scientists were hiding evidence of global warming. This book was mentioned in a 2006 US Senate hearing about climate change, and Peter Doran published a statement in The New York Times explaining that his work was misinterpreted. The British Antarctic Survey and NASA also confirmed the reliability of climate science.
By 2009, researchers combined old weather station data with satellite measurements to create temperature records dating back to 1957. These records showed warming of more than 0.05 °C per decade across Antarctica, with cooling in East Antarctica balanced by warming in West Antarctica of at least 0.176 ± 0.06 °C per decade. This finding was widely reported, and later studies confirmed warming in West Antarctica during the 20th century. Between 2012 and 2013, ice core data and updated records from Byrd Station suggested that West Antarctica had warmed by 2.4 °C (4.3 °F) since 1958, or about 0.46 °C (0.83 °F) per decade. However, some scientists remained uncertain about these results. In 2022, a study found that the central part of the West Antarctic Ice Sheet warmed by 0.31 °C (0.56 °F) per decade between 1959 and 2000, and linked this warming to human-caused increases in greenhouse gases. Cooling in the McMurdo Dry Valleys was confirmed to be a local trend.
Antarctica has continued to warm after 2000. In February 2020, the continent recorded its highest temperature of 18.3 °C, breaking the previous record of 17.5 °C in March 2015. The interior of East Antarctica also showed warming between 2000 and 2020. For example, the South Pole warmed by 0.61 ± 0.34 °C per decade between 1990 and 2020, which is three times the global average. However, changes in wind patterns, such as the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM), slowed or reversed warming in West Antarctica. The Antarctic Peninsula experienced cooling from 2002. While these patterns are natural, past ozone depletion made the SAM stronger than it had been in 600 years of observations. Studies predicted that the SAM would weaken as the ozone layer recovered after the Montreal Protocol, and these changes matched predictions.
Under the most extreme climate change scenario, called RCP8.5, models predict that Antarctica’s surface temperatures will rise by 3 °C (5.4 °F) by 2070 and 4 °C (7.2 °F) by 2100. This would be accompanied by a 30% increase in precipitation and a 30% decrease in sea ice by 2100. The Southern Ocean south of 50° S latitude would warm by about 1.9 °C (3.4 °F) by 2070. RCP8.5 was developed in the late 2000s, but recent research suggests it is less likely than more moderate scenarios like RCP4.5. If a low-emission scenario, similar to the goals of the Paris Agreement, is followed, Antarctica would warm by less than 1 °C (1.8 °F) by 2070. Less than 15% of sea ice would be lost, and precipitation would increase by less than 10%.
Ice loss and accumulation
Different temperature changes in parts of Antarctica cause some areas, especially near the coasts, to lose ice while areas farther inland gain ice. These differences and the difficulty of reaching Antarctica make it hard to find an average trend.
In 2018, a careful study of all previous research by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) found that the West Antarctic ice sheet gained about 53 ± 29 gigatonnes (Gt) of ice in 1992 and 159 ± 26 Gt in the final five years of the study. On the Antarctic Peninsula, the study showed a loss of 20 ± 15 Gt of ice each year, with the loss increasing by about 15 Gt per year after 2000. Much of this loss came from ice shelves. Overall, Antarctica lost 2,720 ± 1,390 Gt of ice between 1992 and 2017, averaging 109 ± 56 Gt per year. This loss added about 7.6 mm (0.30 in) to global sea levels.
A 2021 analysis of satellite data showed that Antarctica lost about 12 Gt of ice each year from 2012 to 2016. This happened because East Antarctica gained more ice than earlier estimates suggested, which helped balance some of the losses from West Antarctica.
East Antarctica can still gain ice even as temperatures rise. Climate change increases snowfall over the region, which freezes and adds to the ice. A 2023 study found that the total area of Antarctic ice shelves grew by about 5,305 km² (0.4%) between 2009 and 2019. This growth in East Antarctica’s largest ice shelves outweighed losses from ice shelves in West Antarctica and the Antarctic Peninsula. While some years show small increases or ice shelf growth, these do not change the long-term trend of overall ice loss in Antarctica.
By 2100, Antarctica is expected to lose enough ice to raise global sea levels by about 11 cm (4.3 in). Other processes, like warm ocean water melting ice sheets, may increase this loss. If warm water flows under West Antarctica’s ice sheet, it could cause ice to melt faster. If ice cliffs taller than 100 m (330 ft) collapse, they could add more to sea level rise. These processes are not yet observed but appear in some models. By 2100, these effects could raise sea levels by 41 cm (16 in) under a low-emission scenario or 57 cm (22 in) under a high-emission scenario.
Some scientists predict even greater losses, but all agree that ice loss in Antarctica will be more severe under higher warming. If global warming stays below 2 °C (3.6 °F), ice loss may continue at the 2020 rate for the rest of the century. However, if warming reaches 3 °C (5.4 °F), ice loss could speed up after 2060, adding 0.5 cm (0.20 in) to sea levels each year by 2100.
Antarctic ice loss adds about 1,100–1,500 billion tons of fresh water to the Southern Ocean each year. This makes the ocean water less salty, which changes ocean layers and affects ocean currents. These changes could speed up upper ocean currents and slow down deeper ones, which depend on salty water from Antarctica. Since the 1970s, upper currents have strengthened by 3–4 sverdrups (Sv; 1 Sv = 1 million cubic meters per second), while deeper currents have weakened by a similar amount.
These changes are partly due to natural cycles, like the Interdecadal Pacific Oscillation, but may worsen with climate change. Climate models suggest that deeper currents may weaken further, while upper currents could strengthen by 20% by 2100. Uncertainty remains because of limited knowledge about future ice loss and how ocean models represent these changes. Some studies predict that ocean circulation could weaken by half by 2050 under extreme warming, with even greater losses later.
It is possible that the Southern Ocean’s circulation could collapse entirely if warming continues, similar to predictions for the Atlantic Ocean’s circulation. However, the Southern Ocean has received less attention than the Atlantic. Research suggests this collapse might happen if global warming reaches 1.7–3 °C (3.1–5.4 °F), but predictions are less certain. Even if this happens, the collapse may not be complete until near 2300. Changes like reduced rainfall in the Southern Hemisphere and declining fisheries may take centuries to fully develop.
Sea levels will continue to rise after 2100, but the rate may vary. Recent reports suggest a median rise of 16 cm (6.3 in) and a maximum of 37 cm (15 in) under low-emission scenarios. Under high-emission scenarios, sea levels could rise by 1.46 m (5 ft) with a minimum of 60 cm (2 ft) and a maximum of 2.89 m (9.5 ft).
Over long timescales, West Antarctica is especially vulnerable because much of its ice is below sea level. If all West Antarctic ice melted, global sea levels would rise by 4.3 m (14 ft 1 in). The collapse of West Antarctica alone could raise sea levels by 3.3 m (10 ft 10 in). This collapse is now considered likely, as it may have occurred during the Eemian period 125,000 years ago when temperatures were similar to today. The Amundsen Sea is warming rapidly, which could make the ice sheet’s collapse unavoidable.
The only way to reverse ice loss is to reduce greenhouse gas emissions and limit global warming.
Situation during geologic time scales
The formation of ice in Antarctica began during the Late Paleocene or Middle Eocene, between 60 and 45.5 million years ago. This process increased rapidly during the Eocene–Oligocene extinction event around 34 million years ago. At that time, carbon dioxide (CO₂) levels were about 760 parts per million (ppm) and had been gradually decreasing from much higher levels in the past. A drop in CO₂ levels, with a critical point at 600 ppm, was the main cause of Antarctic glaciation. This cooling was supported by a period when Earth’s orbit created cooler summers. However, changes in oxygen isotope ratios suggested that the ice age was larger than just the growth of the Antarctic ice sheet alone. The opening of the Drake Passage might have contributed, but models show that falling CO₂ levels were more important.
During the warm early Pliocene epoch, about 5 to 3 million years ago, the Western Antarctic ice sheet slightly decreased, and the Ross Sea opened. However, the land-based Eastern Antarctic ice sheet did not experience significant changes.